Epoxides such as ethylene oxide, propylene oxide, 1,2-butene oxide and the like are useful intermediates for the preparation of a wide variety of products. The oxirane functionality in such compounds is highly reactive and may be ring-opened with any number of nucleophilic reactants. For example, epoxides may be hydrolyzed to yield glycols useful as anti-freeze components or reactive monomers for the preparation of condensation polymers such as polyesters.
Polyether polyols generated by the ring-opening polymerization of epoxides are widely utilized as intermediates in the preparation of polyurethane foams, elastomers, sealants, coatings, and the like. The reaction of epoxides with alcohols provides glycol ethers, which may be used as polar solvents in a number of applications.
Many different methods for the preparation of epoxides have been developed. One such method involves the use of certain titanium silicalite compounds to catalyze olefin oxidation by hydrogen peroxide. This method is described, for example, in Huybrechts et al., J. Mol. Catal. 71, 129(1992), U.S. Pat. Nos. 4,824,976 (Clerici et al.) and 4,833,260 (Neri et al.), European Pat. Pub. Nos. 311,983, 190,609, 315,247 and 315,248, Belgian Pat. Pub. No. 1,001,038, Clerici et al., J. Catal. 129,159(1991), and Notari, in "Innovation in Zeolite Material Science," Studies in Surface Science and Catalysts, Vol. 37, p. 413 (1988).
However, the outcome of synthetic reactions catalyzed by titanium silicalites is highly unpredictable and seemingly minor changes in reactants and conditions may drastically change the type of product thereby obtained. For example, when an olefin is reacted with hydrogen peroxide in the presence of titanium silicalite the product obtained may be either epoxide (U.S. Pat. No. 4,833,260), glycol ether (U.S. Pat. No. 4,476,327), or glycol (Example 10 of U.S. Pat. No. 4,410,501).
The prior art related to titanium silicalite-catalyzed epoxidation teaches that it is beneficial to employ a hydrogen peroxide solution that does not contain large amounts of water and recommends the use of an organic solvent as a liquid medium for the epoxidation reaction. Suitable solvents are said to include polar compounds such as alcohols, ketones, ethers, glycols, and acids. Solutions in tert-butanol, methanol, acetone, acetic acid, and propionic acid are taught to be most preferred. However, hydrogen peroxide is currently available commercially only in the form of aqueous solutions. To employ one of the organic solvents recommended by the prior art, it will thus be necessary to exchange the water of a typical hydrogen peroxide solution for the organic solvent. This will necessarily increase greatly the overall costs associated with an epoxidation process of this type. Additionally, concentration of hydrogen peroxide to a pure or nearly pure state is exceedingly dangerous and is normally avoided. Thus, it will not be practicable or cost-effective to simply remove the water by distillation and replace it with the organic solvent. Since hydrogen peroxide has a high solubility in and high affinity for water, liquid-liquid extraction of hydrogen peroxide from an aqueous phase to an organic phase will not be feasible. Moreover, many of the solvents taught by the prior art to be preferred for epoxidation reactions of this type such as tert-butanol, acetone, and methanol are water miscible and thus could not be used in such an extraction scheme. An epoxidation process wherein a readily obtained oxidant solution containing hydrogen peroxide and an organic solvent which promotes high yields of epoxide products is employed would thus be of significant economic advantage.